Heat exchange method



Patented vSept. 7, I j

V2,092,411 HEAT EXCHANGE' ME'rnon pavia n. reebies, Eureka, com. Application october 19, 1934, serial No. 149,015; 1 ciehn. (ci. 15s-4i) This invention relates generally to methods and is introduced into the inow chamber I2 by means apparatus which utilize an interchange of heat of pipe i3, the inner end of which is formed to between two or more fluids, and which have aflord a spray head I3.' A streamof non-convarious commercial applications, including the densable gas is also introduced into the chamber concentration of liquids by evaporation. I2 by means of conduit 2l. Liquid is removed 5 It is an object of the invention to provide an from the lower chamber I3 through pipe 22 and apparatus of the above character which will afpump l23, while gas and vaporl are removed ford relatively high efficiency with respecttoheat through conduit 24. A baille 2G is shown ex-4 transfer. l V tending down from the lower tube sheet, in order 1o A further object of the invention is to provide to afford better Separating action and in order 1o an apparatus for the concentration of liquids by to avoid drawing of liquid particles into conduit evaporation, which will make possible high con- '14. centrations during a relatively short time period Assuming that, the fill-id in Space l1 is Steam. a of heat treatment. o vapor connection is indicated atl 21, while pipes l5 Another object of'I the invention yis to. make 23 and 29 are indicated for removing condense e i5 possible creation of a vacuum without the use of and small amounts of non-condensable gas, recooling water as in conventional condensing spectively. Where the pressure in chamber I1 methods and apparatus. is below atmospheric, pipe 23 is connected to a Further objects of the invention will appear condensate Dump 01 a blometrio 18g ISO afford a. from the following description in which the preseal, While Dill@` 29 1S connectedbO a Suitable il()v ferred embodiment of the invention has been set vacuum pump. forth in detail in conjunction with the accom- In thesystem illustrated fori-concentrating panying drawing;y i i lliquid, apparatus III can be utilized in conjunction UNITEDv STATES- PATENT ori-icc 'Referring to the drawing: witha further apparatus 3l flor eecting an -ini- Fig. 1 is a diagrammatic view illustrating aptial concentration, thus affording a multiple'vef- 25 paratus incorporating-the present invention. fect evaporator. Apparatus 3l is of a typesimi- Fig. 2 is a cross vsectional detail illustrating `lar to thatdisclosed and claimed in my co-pendthe constructionl of part of the heat exchange ing application Serial No. 698,751, filed November apparatus. 7 20, 1933. Briey, it consists of a housing 32, the The' present invention eifects' a heat transfer upper chamberv 33 of which receives liquid from 30 through a heat conducting wall, such as a metal pipe 34. The lower portion of the houslngcontube, -with heat being absorbed by vaporization nects with a separator 36. Communicating beof a liquid intermingled4 with a current of nontween the chamber 33 and the interior of sepa- 4 condensable gas. The intermingiing of the liquid rator 36 are the' heat transfer tubes 31. The and non-condensable gas is such that a maxiends of. these tubes communicate through tube 35 mum amount ofvaporizlation occurs, in conjunesheets, thereby forming a closed space 3B about tion withl a high rate of heat transfer for a'given the tubes for receiving a heating fluid such as area of heat transferring surface. steam. Thus, a steam line connection to space Before attempting 'a more detailed explanation1 36 is indicated by line 39, and a condensate draw- 40 of my method, I shall first describe the apparatus of! is indicated by line ..Whoh mail be through 40 and system 'illustratedin Fig. 1.` Apparatus In a barometric leg or a condensate pump. Nonis a heat exchanger, which in this instance is condensable gases can also be drawn oil from being utilizedV primarily for the concentration of space 38, as indicated by line'4li. a liquid by evaporation.' lIt consists of a shell II, For controlling theoW 0f liquid into Chamber having the upper portion I2 thereof formed. to 33, I have shown a float control valve 42 which is 45 afford a eas inow chamber. The lower portion actuated in accordance with the level of liquid in I3 of this shell forms an outflow chamber, and the separator 36. This valve controls the rate of is also constructed to function as a separating ow'of liquid through line 34, from the liquid means. Extending between and connecting the supply line 43. In connecting the concentrating y portions I2 and I3 are the heat exchange vtubes apparatus 3l with the heat exchanger I0, liquid 50 I4. The ends of these tubes communicate drawn from the separator 36 throughv the liquid through tube sheets I6, whereby the space I1 outflow pipe 44 is` delivered by pump 46 through surrounding the tubes is isolatedto forma chamline 41 and to the spray pipe I3. The vapor de- A ber for receiving steam or like iiuid. livery conduit 21a from separator 36 connects to The liquid tobe evaporated and concentrated the pipe 21 of apparatus I0. Thus. evolved water 55 vapor from the separator It serves to supply heat to thespace I1 surrounding the tubes |4 of apparatus III, while the liquid concentrated in the evaporator 3| is delivered to the apparatus III for further concentration. Y

Under certain conditions of operation, it is desirable to eect a re-circulation of liquid passing through the apparatus I0. For this purpose I have indicated a valve controlled return line 5|, which serves to divert a portion of the outflow from pump 23 back controlled return pipe 52.

The mode of operation of the apparatus described above, and the carrying out of my method, can be briefly outlined as follows:-Assuming that no re-circulation is carried on through lines 5| and 52, liquid is supplied to the spray pipe I8, and at the same time a stream of non-condensible gas, such as air, is supplied to the conduit 2|. The air stream entering the upper ends of tubes |4 carries with it the particles or drops of liquid, and the velocity of gas flow through each of the tubes I4 is suilcient to cause considerable turbulence. Turbulent iiow through tubes I4 is an important aspect of the present invention, in making possible certain new results; In the rst place, such a turbulent flow causes a maximum amount of relative movement between the air and the particles of liquid, thus causing a sweeping away of vapor being evolved from the liquid, with the result that rapid evaporation of the liquid is promoted. Furthermore, such turbulence causes a continual bombardment of liquid particles upon the inner side walls of the tubes, which bombardment is simultaneously accompanied by a continual whipping-oil of liquid from the inner side walls and back into entrainment with the air. Such action is conducive to good transfer of heat from the walls of the tubes I4 to the liquid being carried through the same. Likewise, such action avoids incrustations or coatings upon the inner walls of the tubes, where the liquid contains solid matter and is being concentrated to a high degree. The net result of such action within tubes I4 is that the material discharged from these tubes consists of the air introduced through conduit 2| together with the remaining liquid and the vapor evolved from the same. A separation between the liquid and the other components is effected in chamber I3, whereby collected liquid is removed through pipe 22, and the air, together with Vapor, is discharged through conduit 24. It will of course be apparent that the heat transfer which is effected in this manner through the walls of tubes I4, and which goes largely toward supplying heat of vaporization for the liquid which is being evaporated, is supplied or absorbed from the steam or like vapor in space I'I surrounding the tubes.

If, in the operation of the apparatus III, a certain amount of the liquid removed through pipe 22 is redelivered to spray pipe I3 through pipe 5|, this returned liquid is resubjected to further evaporation, while the liquid for ilnal delivery is drawn olf at some suitable point in the circuit. Thus as indicated in the drawing, the liquid is being drawn oil' through device 53 for final delivery. In the event the liquid in its treatment within apparatus I0 tends to foam to an undesired degree, it is evident that pump 23 should be capable of handling both foamed and unfoamed components, 53 can be constructed to have a defoaming action. In many instances, however, device. 53 need not be used.

Assuming that the apparatus centration by evaporation, the liquid as partially concentrated in apparatus 3| is delivered to apparatus I0 by pump 46. Likewise, steam or Water vapor which is evolved from the liquid in apparatus 3| is delivered to apparatus I0, thus eifecting an economy in heat consumption. By way of example, with such a system it is feasible to carry the concentration of a liquid. such as milk, to 25% solids in apparatus 3|, and to 45% solids in apparatus I0. Concentration to this degree, and even greater concentration, are obtained without an unduly long time period of treatment, whereby possible injury to organic liquids such as milk is avoided.

It has previously been stated that the noncondensable gas' introduced into apparatus I0 through conduit 2| induces rapid evaporation from the liquid introduced through'spray pipe I8. Thus, a relatively dry gas or air is preferred, having a, substantial moisture-carrying capacity.

In the particular apparatus described above, a considerable vacuum is maintained in space I'I, about the tubes I4. 'Ihus my invention may be employed for such purpose, particularly in localities where a supply of cooling water may be scarce. Maintenance of a vacuum in space I'I also serves to maintain a vacuum in chamber 36, so that apparatus I0 operates as the second evaporating effect of a double effect evaporator, and as a condenser for vapor evolved from the first eiect formed by apparatus 3|.

Iclaim:

In a method of effecting concentration of a liquid by evaporation, where a heat transfer tube is employed, introducing into the tube a liquid to be evaporated, causing a stream of non-condensible gas to iiow through the tube at sutlicient velocity to cause turbulence and maintenance of liquid in the tube in the form of droplets entrained in the turbulent gas iiow, transferring heat through the walls of the tube to cause evaporation' of liquid in transit through the same, and then separating and collecting the/concentrated liquid droplets discharged from the tube apart from discharged non-condensible gas and vapor.

' DAVID D. PEEBLES. 

